Overlay an image with another image, like in photoshop
Well with a bit of exploration I found what I was looking for. The MixRGB Node. I was using the Mix Shader before and that wasn't working at all, then I realized you can't put color nodes in shader nodes...derp.

Anyways if you wanna Mix together different colors or image textures (anything with a color output) just use the MixRGB node and you get all the awesome blend types like in Photoshop (Overlay, Darken, Multiply etc.)